[NORMATIVE-DECODING] option of annex-b/non-annex-b bitstreams

libaom modified to encode/decode AV1 as annex-b or non-annex-b

Encoder option --annexb=0 or 1  (default 0)
Decoder option --annexb

BUG=aomedia:1590
BUG=aomedia:1591

Change-Id: I0f092b45fbf30e689c7fe3c6540d22f497946880
diff --git a/aom/aom_encoder.h b/aom/aom_encoder.h
index e93d081..d54d89f 100644
--- a/aom/aom_encoder.h
+++ b/aom/aom_encoder.h
@@ -663,6 +663,14 @@
    */
   unsigned int monochrome;
 
+  /*!\brief Bitstream syntax mode
+   *
+   * This value indicates the bitstream syntax mode.
+   * A value of 0 indicates bitstream is saved as Section 5 bitstream. A value
+   * of 1 indicates the bitstream is saved in Annex-B format
+   */
+  unsigned int save_as_annexb;
+
   /*!\brief Number of explicit tile widths specified
    *
    * This value indicates the number of tile widths specified